Material working apparatus



March 14, 1967 MOMAHON ETAL 3,309,031

MATERIAL WORKING APPARATUS Filed Dec. 9, 1964 ZK/OF ART INVENTORS 1/5/1691?) I": MC MHHO/V Fin/0 M. 7'0/V5/ United States Patent Ofi ice3,309,031 Patented Mar. 14, 1967 3,309,031 MATEREAL WORKING APPARATUSRichard F. McMahon, Dalton, and Reno M. Tonsi, Lenox, Mass, assignors toJones Division, Beloit Corporation, Beloit, Wis., a corporation ofWisconsin Filed Dec. 9, 1964, Ser. No. 417,073 13 Claims. (Cl. 241-37)This invention relates to a new and improved method and apparatus forcontrolling the operation of a material working device. Morespecifically, the present invention relates to a new method of refinerprocess control in which a process variable is measured to obtain afirst control signal which is then used in conjunction with a secondinstantaneous control signal obtained from the refiner or final controlelement itself and wherein said first control signal is used to controlor modify the corrective action obtained from said second instantaneouscontrol signal.

The present invention is particularly applicable to material defibratingor refining devices for materials such as paper pulp in which therefining operation is controlled in accordance with the amount of workabsorbed by the material in the refiner as measured by a conditionchange of the material which is passed through the refiner.

The control of the quality of the end product of a refining operationmay be accomplished by various control methods such as for exampledescribed in United States Patent Re. 24,185 and United States Patent2,699,095. US. Patent Re. 24,185 describes a control system in which thepower consumed by the driving motor is measured and in which the spacingbetween the refining elements is adjusted according to the powerconsumption variation of the motor. The refining elements are adjustedin such a manner as to hold the power consumption of the motor constant.The disadvantage of this system is that it does not compensate forchanges in motor load occasioned by variations in flow through therefiner. Furthermore, holding the motor power constant does not takeinto account the effect of wear of the refining elements or variationsin consistency and/or other variables of the material fed to therefining apparatus. The above mentioned patent also suggests independentadjustment of the spacing between the refining elements according to ameasure of stock freeness in a subsequent stage of the process. The longtime delay in making such a stock freeness measurement is not tolerablein present day refining operations.

US. Patent 2,699,095 proposes the measurement of temperature rise of thepapermaking stock as it passes through the refiner whereby the refiningelements are spaced relative to each other as a function of thetemperature rise. The disadvantage of this system is that control bytemperature rise alone does not take into account changes in the rate offiow through the refiner and changes of the papermaking stockconsistency. A further disadvantage of refiner control by temperaturerise is that the response time is unduly long mainly because of theinability to instantaneously measure a change in temperature which ismainly due to the inefiiciency of the heat transfer from thepaper-making stock or other material to the temperature measuringdevice.

A third method of refiner control is known as the constant pressurecontrol system. The constant pressure control system operates on theprinciple of maintaining a pre-set pressure between the refiner elementsto give a uniform intensity of refining action. However, variations inrefiner inlet pressure and changes in flow through the refiner require achange in the pressure control set point to maintain uniform refiningconditions.

An ideal control system for a paper stock refiner would not only adjustthe refining element spacing as a function of process variables butwould also control the amount and rate of adjustment by a direct measureof the element spacing as the spacing is adjusted. Such an elementspacing measurement could be made by attaching a slide wirepotentiometer to the element itself or to its adjusting mechanism.However, such a measurement of element spacing is impractical because ofthe wear on the refining elements and other dynamic variables and designconsiderations.

From the above three described control system practical experience withpapermaking stock refiners has shown that refiner control by temperaturerise appears to be the most promising. As pointed out previously,however, the measurement of temperature rise is a time consumingproposition and can only be used effectively when means are provided forproducing an instantaneous corrective signal obtained from the refineror final control element itself and of which the intensity and durationis ultimately controlled by the rise in temperature of the papermakingstock.

The concept of refiner control by temperature rise utilizes theprinciple that a given amount of energy will raise the temperature of amaterial being porcessed by a definite amount. Since papermaking stockas processed in the stock preparation area is at a definite consistencyin the range of from three percent (3%) to five percent (5%) fiber insolution with water, the amount of energy required per unit weight ofvolume of fiber can be calculated by knowing the consistency. As thefiow through the refiner is increased, the amount of additional energyrequired to maintain a given temperature rise of the fiber and watermixture will be in direct proportion to the increase in flow. We may forpractical purposes assume that the consistency (fiber to water ratio) ofthe solution is relatively constant since the material is normallypumped to the refiner from a large holding chest with good agitation andthrough a consistency regulator ahead of the refiner so that theconsistency variations can be kept to a minimum.

In a temperature differential control system as presently known in theart, temperature measuring elements are located in the stock inlet andoutlet lines of the refiner and such measuring elements are preferablylocated as close as possible to the inlet and outlet ports of therefiner housing. The two temperature signals obtained from thetemperature measuring elements are fed to a temperature differenceconverter which produces an output signal proportional to thetemperature rise of the stock across the refiner. This signal is fed toa controller which compares the signal from the temperature differenceconverter with a predetermined set point signal value, and causes thecontroller to reposition refiner elements whenever there is a differencebetween these two signals. In accordance with normal control practicessuch a controller has a built-in feedback network which feeds a signalback into the cont-roller as a function of the output signal of thecontroller. This feedback signal is not infiuenced by the actual orphysical corrective movement of the correcting device nor by the actualphysical change in refiner element spacing. In principle, the controllerwill send a corrective signal to the corrector and the built-in feedbacknetwork will notify the controller that the corrective signal has beendispatched to the corrector. Upon being thus notified by the internalfeedback signal the controller will be balanced and its correctivesignal will be reduced to some predetermined constant value to which thecorrector does not respond. However, due to the effects of inertia andfriction of the moving parts in the corrector, a corrective signal sentby the controller may not have been sufficient to obtain the correctiveaction actually required to correct the erratic process variable.Accordingly, since the erratic variable has not been entirely correctedthe sensor will continue to send a signal to the controller which onreceipt of the feedback signal is in physi al balance. The delayed errorsignal will build up in intensity as time goes by and will again upsetthe controller after which the cycle is repeated. Therefore, acontroller which is equipped with a built-in feedback signal willrequire several cycles to obtain the desired corrective action for thistype of control system. In addition, it should be borne in mind that asubstantial amount of time may lapse before the corrective signal (whichis a function of temperature rise of the material in the refiner) comesto a peak value and thus produces the amount of correction actuallyrequired due to a change of operating conditions.

Since 'the most common variable in a stock refining system is a changein flow ratethrough the refiner, such a change in flow will not onlyresult in a variation of the.

temperature'in the refiner but also in a change in the power consumptionof the motor which drives the refiner since more or less workwill beabsorbed by the stock.

Such a change in power consumption of the driving motor can beconsidered instantaneous and a corrective signal obtained therefrom willactivate the correctorimmediately and substantially earlier than wouldbe possible with a corrective signal obtained as a function of atemperature variation in the refiner. Such an instantaneous correctivesignal would eliminate the transfer lag inherent in a temperaturecontrol system.

We have discovered that an ideal refiner control process can be obtainedby combining the temperature change variable with the power changevariable into a single closed control loop. By thus combiningtemperature change with its associated power change of the drive motorwe are-able to obtain. an immediate corrective signal as a function ofthe power change, The temperature change signal which develops at alater time and at a slower rate can be usedto control the instantaneouspower change signal as soon as the refiner element spacing has beenproperly adjusted. H

Accordingly, an important object of the present invention is to providean automatic closed loop controLsystem which embodies a process variablemeasuring device, an automatic proportional control device, and anexternal feedback measuring device for closing the control loop.

Another object of the invention is to provide a closed loop controlsystem for a paper stock refiner comprising means for measuring aprocess variable and continually comparing said variable with apredetermined set point value to obtain, a first control signal, meansoperatively connected to said refiner to obtain a second instantaneouscontrol signal which is in direct proportion to said process variableand said first control signal, networkmeans for computing thealgebraicsum of said first and second signals to obtain a final control signal,and means operatively, connected to said refiner for adjusting saidrefiner as a function, of said final control signal.

A further object of theinventionis to provide a closed loopcontrolsystem for a paper stock'refining device,

which includes, a first temperature responsive means operativelyconnected to the inlet portion of said refining device whereby the inlettemperature of the material processed by said device is continuouslymeasured, second temperature responsive means operatively connected tothe outlet of said refiningdevice whereby the outlet temperature of thematerial is continuously measured, means connected to said first andsecond temperature responsive means to develop a first signalproportional to the signal as a function of the power change. The.temperature change signalwhich develops at a later time and at a slowerrate can be used to control the instantaneous power change signal assoon as the refiner element'spacing has been properly adjusted.

Accordingly, an important objectof the presentinvention is to provide anautomatic closed loop control system which embodies a process variablemeasuring device, an automatic proportional control device, and anexternal feedback measuring device for closing the control loop.

Another object of the invention is to provide a closed loop controlsystemfor a paperstockrefiner comprising means for measuring a processvariable and continually comparing said. variable with a predeterminedset point value to obtain a first control signal, means operativelyconnected to said refiner to obtain a second instantaneous controlsignal which is in direct proportion to said process variableand sa-idfirst control signal, network means for computing the algebraic sum ofsaid first and secondsi-gnals to obtain a final control signal, andmeans operatively connected to said refiner for adjusting said refineras a function of said final control signal.

A further object of the invention is to provide a closed loop:controLsystem. for, a paper stock. refining device which includes afirst temperature responsive means operatively connected to the inletportion of said refining device whereby the inlet temperature of thematerial work absorbed by the stock in said refiner thereby clevelopinga :second instantaneoussignal proportional to said work absorbed, acontroller having an input network for receiving said first signalandsecond power responsive signal computing network for receiving saidsecond instantaneous signal from said external power sensing means, andmeans for comparing said first signal with said second signal whereby acontroLresponse is generated to direct a motor means whereby. therelative spacing of the refining elements of said refining device can becontrollably varied,

A feature of the present invention is to provide a closed loop controlsystem for a continuous flow paper stock refining apparatus whichincludes means directly sensing the work absorbed by the paper makingstock, means for measuring the temperature rise of the papermaking stockas it flows through :the refining apparatus, and a controller responsiveto said temperature and work sensing means for adjusting the effect ofthe refiner on the stock so as to maintain the operating conditions ofthe refiner at predetermined constant values.

Other objects and advantages will appear from time to time as thisspecification proceeds with the reference to the accompanying drawingsinwhich FIG. 1 is a diagrammatic representation of a control system for apaper stock refiner as used in. the prior art; and

FIG. 2 isa diagrammatic. representation of a control system inaccordance with the principles of. the present invention.

FIG. 1 shows a prionart-temperature control system a bridgecirouit. Anunbalanced condition due to differ-- ences in temperature at inlet 13and outlet 14 will cause the bridge circuit to produce a signalproportional to thetemperature difierence sensed by the elements 15 and16. The signal produced by temperature difference is applied to aconverter 17, which can be either a conventional differential amplifier,or a high impedance direct current amplifier. The amplified signal fromthe converter 17 is then sent to a controller 18 which, in turn,converts the electrical signal to a corresponding pneumatic signal. Thenewly derived pneumatic signal is linearly proportional to theelectrical signal from the converter 17. The pneumatic control signal isthen applied to a motor M through a pneumatic line 19. The motor M isconnected to the movable refining element 12 whereby the spacing betweenthe refining elements 11 and 12 may be controlled to maintain thetemperature dilferential between the inlet and outlet ports of therefiner at a preselected constant value.

The operation of this prior art control system may be best understood byassuming that the temperature difference of the material between theinlet and outlet 13 and 14 respectively is disturbed by a sudden changeof flow rate through the refiner 10. Such a change in flow rate willresult in a temperature difference signal AT being developed by thetemperature difference converter 17. The converter 17 will send aproportional signal to the controller :18. The operation of thecontroller 18 may be best described by assuming that it contains apivotally mounted flapper 20 which will be caused to pivot in aclockwise direction due to the signal sent to it by the converter 17. Asthe flapper 20 rotates in a clockwise direction it will move away froman orifice 21 in the line 19 thus causing a change in air pressure insaid line 19. However, the controller 18 contains an internal feedbackcontrol line 22 which sends an appropriate signal to the other side ofthe flapper 21) thus causing it to resume its balanced position. Theinternal feedback signal is directly proportional to the signaltransmitted to the refiner element positioning device M via the line 19.It will be appreciated that if the disturbance in fiow rate through therefiner is relatively small the change in disparity between the inletand outlet temperature of the refiner will be relatively small and maynot be sufficient to overcome the backlash in the gear mechanism usedfor moving the refiner element 12. Such a gear backlash is inherent inevery mechanical positioning device and is in effect a built-in deadband within which the change in temperature between the inlet and outletof the refiner is not controllable and may very at random. Furthermore,it will be appreciated that the internal feedback signal is notinfluenced by the actual or physical corrective movement of thecorrecting device M In principle, the controller 18 sends a correctivesignal to the correcting device M and the feedback network 22 willnotify the controller that the corrective signal has been dispatched tothe corrector M thereby balancing the controller and counteracting itscorrective signal. With this type of control system, which is entirelybased on a control signal obtained from a variation between the inletand outlet temperature of the refiner, it will be readily apparent thatthe corrective action is not instantaneous and may require a substantialamount of time due to the slow response of the temperature sensingelements 15 and 16.

Referring to the improved mechanism of the present invention, as shownin FIGURE 2, the inlet 51 has a temperature sensing device 59 attachedthereto whereby the inlet temperature of the stock being processed iscontinuously measured. The outlet 52 has a temperature measuring device60 attached thereto whereby the outlet temperature of stock iscontinuously measured. The temperature measuring devices 59 and 60 forman integral part of a conventional bridge circuit, with the remainingtwo legs of the bridge built into the converter 61. The converter 61 isof a type which will be recognized to those skilled in the art from theforegoing description, preferably such as a Leeds and Northupdifferential tem- 6 perature thermohm transmitter No. 41901119997 6-().

Upon comparing the respective temperatures of elements 59 and 60, theconverted 61 will develop a control signal which has a valueproportional to the temperature difference sensed by the input element59 and output element 60. I

As mentioned hereinabove, the converter 61 may be in the form of acommercially available resistance to current converter which may alsoinclude an amplifier 62 for amplifying signals applying thereto.

Connected to the motor M is an external power sensing means W, whichwill be recognized from the foregoing description, preferably of a typesuch as a Lincoln Thermoconverter, Leeds and Northrup catalog No. 10,-730. The function of the power senser W is to produce correspondingvoltage signals which are proportional to the power consumption of themotor M The power input to motor M is proportional to the work absorbedby the stock in the refiner 50 and hence proportional to the temperaturerise of the stock. It can be seen therefore that the sensor W developsan instantaneous signal which is proportional to the input power to themotor M and which signal is proportional to the temperature rise of thestock. Connected to the power senser W is a converter C for convertingthe voltage signal from power senser W to a current signal similar tothe current signal obtained from the comparator 61 and amplifier 62. Theconverter C is of a type which will be recognized from the foregoingdescription preferably such as a Leeds and Northup converter, catalogNo. 41901-3- 10O456O.

The signal from amplifier 62 and the signal from the converter C areapplied to a controller K, which is preferably a type such as a Leedsand Northru Model C controller. The controller K is further providedwith a variable reference signal generator R for generating apredetermined desired signal as a function of the desired mechanicalenergy to be absorbed by the fibrous material as it is being processedby the refiner 50. It can be seen, therefore, that the mechanical energyabsorbed by the fibrous material in the refiner 50 is a direct functionof the temperature increase of the fibrous materiaL. The referencesignal from the network R together with the signal from the input I arefed to an error signal generator E, which is a differential amplifier.The error signal generator E develops a signal corresponding to thealgebraic sum of the signals received from the input network I and thereference generator R,,. The error signal generator E will develop asignal as soon as the value of the signal fed into the input network Ideviates from the predetermined value of the signal applied to the errorsignal generator E by the variable reference signal generator R Thesignal from converter C, which also corresponds to the instantaneouspower change of the motor M is fed to a power responsive signalcomputing device or network 65. The computing network 65 is an integralpart of the controller K, and which computing network includes variableproportional and automatic reset circuits whereby the value of the inputsignal generated therein is linearly proportional to the external powersignal or external intelligence and is further linearly proportioned tothe time integral of said external intelligence. The

computing network 65 includes means for comparing the error signal fromthe converter C with the error signal from the generator E. The meansfor comparing the error signals from the converter C and the generator Emay schematically be represented by means of a flapper member 66 whichis pivotally mounted at 67. The signal from the converter C (which isinstantaneous) will cause the flapper 66 to rotate in a clockwisedirection thus causing an imbalance of the flapper 66 which in turn willresult in an immediate signal 68 to be sent to the refining elementpositioning motor M The signal from the error generator E (which is afunction of the change in disparity between the inlet temperature T1 andthe outlet temperature T2 of the refiner 54?) will attempt to balancethe flapper member 66 thus reducing the output signal 68 and thereby theaction of the refiner element positioner M However, as previouslyindicated the signal from the generator E is developed at a slowerratethan the signal from the converter C. Moreover the signal from theconverter C is instantaneous in nature and dieliminated; the time delaywhich is unavoidable when the temperature change in the refiner is usedas the primary control means.

In summary, it will be appreciated that after the instantaneous powerchange signal. is received by the flapper element 66 from the converterC there will be a change in the feedback side of the controller K and asignal 68 will 'be sent to the refining element positioner M long as theupset remains in the controller the signal to the COI'I'ClIOIfl M willcontinue. Therefore, the controller must be balanced which balance isachieved by the change in the signal received by the flapper element 66from the amplifier 62. As soon as the signal from'the amplifier balancesthe flapper 66 the corrective action by the positioner M becomes zero.The main function therefore,

of the external feedback signal from the power source M is to stabilizethe controller and to controlthe amount and rate of adjustment of therefining element spacing by a directmeasure of the element spacing asthe spacing is adjusted.

With external feedback of actual changein workabsorbed by the stock orpower input into the drive motor M the controller is immediatelynotified of a change in flow condition through the refining machinewhich results in instantaneous corrective action. In addition, thecontroller is notified of the actual corrective action that has takenplace because as soon as the corrector M; changes the spacing betweenthediscs 53 and 54 the power input into the motor M will change-therebychanging the signal sent to the controller K by the converter C. Thisexternal feedbacksignal from the converter C therefore notifies thecontroller of the actual corrective action that has taken place andcontrols the amount and rate of the corrective action. With aninternal'feedback system as previously described with respect to FIGURE1 the controller is notified of the corrective action that has beendemanded by the error signal from the temperature difference converter17. With the use of external feedback from the final control elementitself our invention therefore results in fast and effective return tonormal operating conditions Without having to rely on time consumingtern perature measuring cycles as described above with respect.

to the prior art control system of FIGURE 1.

Although we have herein described our invention as being used inconnection with a paper stock refining device it will be apparent thatthe principles of the invention are by no means limited to such device.Obviously our method may be equally well applicable to grinding ordefibrating operations of a wide range of materials and, the

term refiner as used in the claims is meant toinclude material-workingdevices of the type in which a physical change of the material is afunction of the'amount of work absorbed by said material, which workabsorption can be measured by a differential in temperature, pressure,flow or any other variable.

We claim:

1. A control system for a material working-device comprising:

means for measuring a change in temperature rise of the material, and

means for measuring a change in work absorbed by the material and meansresponsive to said change in temperature rise and said change in workabsorbed for adjusting the effect of the materialworking device on thematerial toward a predetermined value.

2. A stock refinining, apparatus comprising:

a refiner having'an input and output with a stock solution flowingtherethrough,

control means for varying the refining action of said an inputtemperature responsive means and an output temperature responsive means,

means for measuring the work absorbed by said stock,

and

control means including said temperature responsive means and said workmeasuring means to control said control means for said refiner.

3. In a control mechanism for a defibrating device,

means defining an inlet and an outletwhereby fibrous material may beintroduced into and removed from said defibrator,

means within said ,defibrator defining opposed close running defibratingsurfaces including means for introducing said material therebetween,

first motormeans operatively attached to at least one of said surfacesfor rotationally driving said surface whereby said material is workedmechanically and resulting in a temperature increase of said material,

first temperature responsive means operatively connected to said inletwhereby the inlet temperature of thefibrous material is continuouslymeasured, a

second temperature responsive means operatively connected to said exitwhereby the exit temperature of the fibrous material is continuouslymeasured,

means connected to said first and second temperature responsive means tocompare the value of said first I and including means for convertingsaid signal to be.

compatible in nature to said first signal, second motor meansoperatively connected to at least one of saiddefibrating surfaceswhereby its relative position with respect to'the other of said surfacescan be controllably varied to maintain a relatively constant stock,quality under varying flow rates through said defibrator, a controllerhaving:

an input network for receiving said first signal, a variable referencesignal generator having means for generating a predetermined desiredsignal. as a function of desired mechanical energy to be absorbed bysaid fibrous material, means operatively connected to said input networkand said reference generator for developing an error signalproportional'to the algebraic. sum

means for comparing said error signal with said.

power signal whereby a control response is generated to direct saidsecond motor means thereby controllably' varying the relative positionof said defibrating surfaces whereby said first signal is maintained ata predetermined value.

4. A control system for maintaining a variable function at apredetermined value comprising:

first and second motors connected to a processing unit,

said variable function being indicative of characteristics of materialprocessed by said processing unit,

means connected to said first motor for developing a primary signalcorresponding to changes in the variable function,

control means for receiving said primary signal to provide a controlsignal therefrom,

said control signal from said control means being applied to said secondmotor,

and sensing means connected to the processing unit for developing asecondary signal corresponding to changes of the variable function,

said secondary signal being applied to said control means for comparisontherein with said primary signal to effectively change said controlsignal applied to said motor.

5. A control system for a refiner mechanism with a material inlet andoutlet and having relatively rotating refiner members for defibratingmaterial comprising:

a drive motor connected for driving one of the refiiner members inrotation,

a control motor connected to the members for controlling the refiningaction of the members,

power means connected to said drive motor for developing primary signalscorresponding to changes in motor operation due to changes incharacteristics of the material from a predetermined value,

control means for receiving said primary signal to produce signalstherefrom,

said control signals being applied to said control motor to change therefining action of the members, sensing means positioned to sense theconditions of the material in the refiner for producing a secondarysignal corresponding to changes of said material caused by said controlmotor,

reference signal means producing a constant reference signal,

and means for comparing said reference signal with said secondary signalto produce a feedback signal sufficient to eliminate said control signalwhen said constituent of material is at said predetermined value.

6. The control system of claim in which said sensing means has a slowerspeed of response than said power means.

7. In a material refining control system for maintaining acharacteristic of material at a predetermined constant value comprising:

a refiner having a work chamber for processing the material,

input and output means connected to said work chamber for supplying rawmaterial to said work chamber and for receiving finished material fromsaid work chamber, stationary means in said work chamber,

rotating means in said work chamber for applying work to the materialthereby refining the material as it passes between said stationary meansand said rotating means, a drive motor for rotating said rotating means,a control motor for controlling the distance between said stationarymeans and said rotating means,

power means connected to said drive motor for developing primary signalscorresponding to changes of the characteristic of the material from apredetermined value,

a control means for receiving said primary signals to produce controlsignals therefrom,

said control signals applied to said control motor for changing thedistance between said stationary means and said rotating means,

sensing means connected between said input and said output means forproducing a secondary signal corresponding to changes of thecharacteristic of the material in said work chamber,

reference signal means in said control means, and

means for comparing said reference signal with said secondary signal toproduce a feedback signal,

said feedback signal being applied to the control signal and beingsufficient to eliminate the control signal from said control motor whenthe characteristic of the material is at a predetermined value.

8. The material refining control system of claim 7 in which saidcharacteristic of material which is maintained at a constant value istemperature.

9. A paper stock refiner comprising in combination:

refiner plates positioned to form a refining zone therebetween,

a drive motor connected to one of the plates for driving it in rotation,

a control motor connected to control the distance between said plates,

a first signal means measuring the power input of the drive motor,

a second signal means measuring the temperature differential of stockflowing into and out of the space between the refiner plates, and

means for receiving the signals produced by said first and second signalmeans and operatively connected to said control motor for controllingthe distance between said plates.

10. A paper stock refiner comprising in combination:

refiner plates positioned to form a refining zone therebetween,

a drive motor connected to one of the plates for driving it in rotation,

a control motor connected to control the distance between said plates,

a first signal means measuring the power input of the drive motor,

a second signal means measuring the temperature differential of stockflowing into and out of the space between the refiner plates, and

means for receiving the signals from said first and said second signalmeans and comparing said signals,

said receiving means generating an error signal as a function of thedifference between said first and second signals and supplying saiderror signal to the control motor for controlling the spacing betweenthe plates as a function of said error signal.

11. A paper stock refiner comprising in combination:

refiner plates positioned to form a refining zone therebetween,

a drive motor connected to one of the plates for driving it in rotation,

a control motor connected to control the distance between said plates,

a first signal means measuring the power input of the drive motor,

a second signal means measuring the temperature differential of stockflowing into and out of the space between the refiner plates,

means for generating a constant reference signal,

means for comparing said reference signal with the signal received fromsaid second signal means and prodllcing a feedback signal, and

means comparing said feedback signal with the signal received from saidfirst signal means, and connected to said control motor for operatingthe control motor to change the spacing between said plates until thefeedback signal is adequate to eliminate the signal from said firstsignal means.

12. The method of controlling the refining operation of a paper pulprefiner by changing the spacing between refining plates which comprisesmeasuring the power in-:

put to the refiner, measuring the temperature differential of the stockflowing into and out of the refiner, and controlling thedistance-between plates as a function of the work input and temperaturedifferential.

13. The method of controlling the output of a paper pulp refiner havingrelatively rotating plates by controlproducing. a second, signal whichis a function of tem-- perature differential between the stock enteringand I the stock leaving the refiner;

producing a constant signal and comparing it with the second signal oftemperature differential to produce a feedback signal, and

comparing the feedback signal with the first signal of power input andcontrolling the distance between the plates as a function of thedifierence.

No references cited.

WILLIAM W. DYER, JR., Primary Examiner. G. A. DOST, Assistant Examiner.

1. A CONTROL SYSTEM FOR A MATERIAL WORKING DEVICE COMPRISING: MEANS FORMEASURING A CHANGE IN TEMPERATURE RISE OF THE MATERIAL, AND MEANS FORMEASURING A CHANGE IN WORK ABSORBED BY THE MATERIAL AND MEANS RESPONSIVETO SAID CHANGE IN TEMPERATURE RISE AND SAID CHANGE IN WORK ABSORBED FORADJUSTING THE EFFECT OF THE MATERIAL WORKING DEVICE ON THE MATERIALTOWARD A PREDETERMINED VALUE.